1. Field of the Invention
This invention relates to improving the heat stability of acrylamide functional polydiorganosiloxanes containing compositions.
2. Background Information
Polyorganosiloxanes are known to have valuable properties for protecting surfaces from environmental attack such as from weather, chemical, cold, and heat. However, improvement is still sought, so that, polyorganosiloxane containing materials can be used in harsher environments. Polyorganosiloxanes provide electrical insulating properties which make them useful in the electronics industry for coatings, encapsulants, and potting materials. For example, a printed circuit board may find utility in an engine of an automobile or other vehicle, but the operating temperatures may be too high for prolonged exposure and the polyorganosiloxane containing materials may not adequately maintain their functional properties over prolong use. However, if one can increase the serviceable temperature of the polyorganosiloxane containing material, maybe a coated printed circuit board might be useful for applications where it will be exposed to high temperatures. The polyorganosiloxane containing material should maintain sufficient physical integrity to protect the device it is covering and also it should not release degradation products in amounts which may harm delicate instrumentation.
The use of polyorganosiloxane containing materials which will cure by exposure to ultraviolet radiation provide the advantages that they are fast curing, give off low amounts of volatiles during curing, are readily applicable to automation, cure at low temperatures, and provide reduced energy costs. These are some of the reasons for today's industry wanting to use both polyorganosiloxane containing material and ultraviolet radiation curing. However, many of the polyorganosiloxane compositions which cure by exposure to ultraviolet radiation have relatively low tolerance to prolonged exposure to high temperatures without degrading or loosing their physical properties. To make them more desirable for applications protecting surfaces from harsh environments during and after exposure to high temperatures, the heat or thermal stability needs to be improved. Therefore, a search was conducted to find a means for increasing the serviceable temperature of ultraviolet radiation curable polyorganosiloxane compositions. The means should overcome the effects of exposure to high temperature, such as loss of mechanical strength and toughness, embrittlement and cracking, and reduction in electrical properties.
In our copending application Ser. No. 07/335,639, filed Apr. 10, 1989, now U.S. Pat. No. 5,036,114, the heat stability at 150.degree. C. of acrylamide functional polydiorganosiloxanes can be improved by the addition as heat stability additives zinc naphthenate, stannous octoate, and organotitanates.